China bird flu case puzzles experts

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BEIJING — A new case of bird flu in China’s capital, a 4-year-old boy who displayed no symptoms, is adding to the unknowns about the latest outbreak that has caused 63 confirmed cases and 14 deaths, health officials said Monday.

The boy, who tested positive for the H7N9 virus, is considered a carrier of the strain and has been placed under observation to see if he develops symptoms, health authorities said.

Medical teams found the boy in a check of people who had contact with a 7-year-old girl, who was confirmed as Beijing’s first case of H7N9 over the weekend: a neighbor of the boy bought chicken from the girl’s family.

Zhong Dongpo, Beijing Health Bureau deputy director, said that as puzzling as the case is, the boy adds another data point to medical experts limited understanding of H7N9.

‘‘This is very meaningful because it shows that the disease caused by this virus has a wide scope. It’s not only limited to critical symptoms. There can also be slight cases, and even those who don’t feel any abnormality at all. So we need to understand this disease in a rational and scientific way,’’ Zhong said at a news briefing.

The H7N9 strain was not previously known to infect humans before cases turned up in China this winter, and Zhong and other medical experts said no evidence exists that the virus can be passed from one person to another.

Close contact with infected birds is a likely source of transmission. Infected poultry display slight or no symptoms, making the virus hard to detect, unlike the H5N1 strain which kills birds and raged across the region in the middle of the last decade.

The appearance of cases with mild or no symptoms in humans could make tracing even more difficult, but may also mean that many people infected do not get seriously ill and recover quickly, making the virus is less deadly than it appears.